EARTH Magazine: Dating of Landslides Around Oso Reveals Recurring Patterns

EARTH Magazine

From EARTH Magazine, June 21, 2016  --  In March 2014, 43 people were killed when 7.6 million cubic meters of mud and debris violently engulfed a portion of Oso, Wash., after a period of heavy rain. The region where this occurred is characterized by impermeable clay and silt deposits, sometimes measuring more than 200 meters thick, which formed 16,000 years ago when an ice sheet covered the region. These deposits and the addition of a wet, rainy climate makes the Stillaguamish River Valley ripe for more landslides. 

While the soil deposits, topographical relief and climate presented a well-known hazard to the region, the devastating Oso slide made determining how many other landslides had occurred in the past in the valley imperative. So geologists set about mapping and dating distinct landslide deposits in the valley. EARTH Magazine brings you the story of a team of geoscientists that are determining when the many landslides in the Stillaguamish River Valley occurred and what the recurrence rates are. What they have found suggests that landslides may be occurring more frequently now than ever before. Using this information, the team believes the hazard potential of the region, and others like it, can be better assessed. Discover the ages of the Stillaguamish River Valley landslides, and what that may mean for valley residents in EARTH Magazine:

The May Issue of EARTH Magazine continues exploring the science behind the headlines from around the world. We look at new fossils that illuminate the "hobbit's" evolutionary history, how scientists are using radar to find unmarked graves and how new technologies are helping oceanographers map the seafloor in HD. Read these stories, and many more at